Selection and evaluation of materials for future system-on-package (SOP) substrate

This work deals with the selection and evaluation of candidate materials as a future base substrate for SOP. New composite materials using advanced fiber clothes and fillers were fabricated and tested to evaluate the increase in performance compared to conventional glass-epoxy substrates (FR-4). Composites built with advanced carbon-cloth having a negative thermal expansion coefficient (CTE) yielded a composite CTE of <3 ppm/°C. The composites have 2-3 times higher modulus than conventional FR-4. In order to evaluate materials with further higher modulus, metal matrix composites Al/SiC with low CTE of 7 ppm/°C and high modulus of 220 GPa were also considered. The thermomechanical reliability of the electrical interconnections was evaluated after assembling flip-chips on three different substrates by subjecting test vehicles to thermal shock treatments. The failure modes in different substrates were analyzed with optical microscopy. The stresses in the solder joints and dielectric layer were also estimated with analytical and finite element models (FEM)